This invention relates to a lock-up preventing brake force controller for vehicles, particularly for automotive vehicles, wherein the pressure medium can be supplied from a pedal-operated master brake cylinder to the operating cylinders on the wheel brakes.
Anti-lock regulators have been known which operate in most cases with the aid of electronic components, whereby the safe functioning of these arrangements is, under certain circumstances, rendered questionable. The invention contemplates providing a brake force controller of a mechanical type having a simple kind of construction, which is safe in operation and which readily ensures the continuation of the braking process even if the controller has failed.
In accordance with this invention, means are provided for ensuring that the resultant brake pressure on the operating piston in the operating cylinders of the wheel brakes can be controlled by means of a control element in dependence on the relative movement between the brake lining and the brake disks or brake drums detected by a measuring element. In this connection, a solution is preferred according to which a control piston is arranged between the master brake cylinder and each wheel brake, the front face of this control piston being exposable to the pressure in the master brake cylinder and the rear face of this control piston being in communication with the front face thereof by way of a communicating connection, with a control element disposed in said communicating connection for controlling flow therethrough in dependence on the relative movement of the brake lining and brake disks or drums.
Thus, the invention proceeds quite generally along the lines of producing the operating force for the brakes by a more or less bilateral exposure of the control piston to the pressure determined in the master brake cylinder, and therefore also controlling such operating force. The relative movement between the brake disk or brake drum and the brake lining serves as the measuring element, in this connection. This method can be accomplished in a technically simple and functionally safe manner and does not give rise to any objections. In case the control mechanism fails, there will always exist a contact force on the brake due to the difference in surface area at the control piston, so that the braking effect will be retained in any event.
A further simplification of the proposed system is achieved by a preferred embodiment of the invention according to which the operating piston provided in the wheel brake cylinder constitutes itself simultaneously the control piston, and according to which the connecting lines from the spaces on its front and rear faces terminate in a cylinder on either side of a piston provided as the control element and having an axial bore passing therethrough. Thus, the arrangement here is such that the control element, in its central position, frees the connection between the two piston sides, optionally under a corresponding throttling action, i.e., releases the brake and, when deviating from this central position toward one of the two sides, blocks this connection, i.e., makes it possible to actuate the brake. This blockage is effected in both directions of rotation of the brake disk or the brake drum. It is then furthermore suggested that the space on the front face of the control piston and the space on the rear face thereof are connected by means of respectively one line under throttling action with a compensating vessel, and that the throttling of the line on the front side is stronger than that of the line on the rear side.
In another preferred embodiment according to this invention, the control piston is fashioned as a special differential piston, the large piston area of which is exposed to the pressure from the master brake cylinder and the small piston area of which serves to supply pressure to the wheel brake cylinder, and wherein the space accommodating the differential piston area is connected via the adjusting element with the space accommodating the large piston area, as well as by way of a throttle valve with a brake fluid container. By an appropriate choice of the area proportion, a servo effect can here be attained at the same time. In general, the adjusting member will be fashioned and/or operated in the same way as in the the preferred embodiment mentioned hereinabove. However, a two-edge control operation can also be introduced by constructing, according to a further suggestion of the invention, the adjusting member as a dual piston, the first piston section of which regulates the bypass line and the second piston section of which regulates the line to the brake fluid container so that the former is open if the latter is closed, and vice versa.
As for the construction of the measuring element, the invention proposes to place a lever serving as the measuring element in frictional contact with each brake drum or brake disk, this lever being held resiliently in its central position and acting on the adjusting element directly or by means of a solenoid. The lever can directly engage the piston rod of the adjusting control piston. It is also contemplated to fashion the measuring element as a switch which actuates a solenoid in the release position. Also other sequence-type follow-up arrangements are suitable in this connection.